Dichroic dye, and liquid-crystal composition and liquid-crystal display element containing the dye

ABSTRACT

A dichroic azo dye characterized by having a trifluoromethyl-substituted biphenyl framework and being represented by the following general formula, and a guest-host liquid-crystal composition and a liquid-crystal display element each containing the same and having a high order parameter throughout the whole light absorption wavelength range, are provided: ##STR1## (wherein A and B each independently represents an optionally substituted alkyl group, phenyl group or cyclohexyl group; X and X 1  each independently represents a methylene group or a carbonyl group; and R 1  to R 12  each independently represents a hydrogen atom, a halogen atom, a methyl group or a methoxy group, or R 2  and R 3 , R 5  and R 6 , R 8  and R 9 , and R 11  and R 12  may be bonded to each other to form an aliphatic, aromatic or nitrogenous aromatic ring which is a five-membered or larger-membered ring).

This application is a 371 of PCT/JP96/02316 filed Aug. 20, 1996.

TECHNICAL FIELD

The present invention relates to a novel yellow dichroic azo dye, aliquid-crystal composition containing the same, and a liquid-crystaldisplay element using the same.

BACKGROUND ART

Various display modes for liquid-crystal display elements have beenproposed so far, besides the twisted nematic (TN) display mode, thesuper-twisted nematic (STN) mode, and the like. Among those, theguest-host (GH) display mode which employs a dye dissolved in a liquidcrystal is currently widely used in automotive and other display panelsbecause of characteristics thereof such as a wide viewing angle andbrightness, and is receiving attention because of its suitability for,e.g., reflection type displays for use in portable informationapparatus.

Dyes for use in the GH mode are required to be excellent in

1) dichroism,

2) solubility,

3) light resistance, and

4) coloring power.

Since dye dichroism or order parameter, among those properties, directlycorrelates with the display qualities, such as contrast, of guest-hostliquid-crystal display elements, there has hitherto been required aguest-host type liquid-crystal composition having a high orderparameter. In particular, a guest-host liquid-crystal composition havinga high order parameter which comprises a new host liquid-crystalcomposition such as a fluorinated one and which can be used inactive-matrix operation type LCDs and the like is recently required.

Azo dyes having a biphenyl framework are advantageous in that they havea high extinction coefficient (coloring power), and that since azostructures can be simultaneously incorporated respectively on both sidesof the biphenyl framework, the cost of the production thereof is low anda dye having a large molecular length so as to be suitable for use withliquid crystals can be easily produced. In U.S. Pat. No. 4,610,803 thereare shown various dichroic trisazo dyes including the dyes of thestructures shown below, which are given therein in Examples 2 and 3, asspecific examples of yellow dichroic dyes having an azo group on eachside of a biphenyl framework.

Example 2 ##STR2## Example 3 ##STR3##

However, such azo dyes having a biphenyl framework have had considerablelimitations on the production and use thereof because of the hightoxicity (carcinogenicity and mutagenicity) of the benzidine compoundsused as starting materials therefor.

On the other hand, guest-host liquid-crystal compositions eachcomprising a mixture of a host liquid crystal and a single dichroic dyehave had a problem that because of the structure, etc., of the dichroicdye used, the order parameter thereof is not constant throughout thewhole light absorption region and often decreases in a light absorptionwavelength range apart from the main absorption wavelength (λ_(max))This problem has led to the phenomenon in which a guest-hostliquid-crystal composition containing various dichroic dyes incombination so as to have hues such as black, brown and dark blue has areduced order parameter in the wavelength spectral range where lightabsorption by the individual dichroic dyes overlaps, and the reducedorder parameter renders the whole liquid-crystal composition to haveinsufficient contrast. Such a phenomenon is noticeable when dichroic azodyes having a wide light absorption wavelength range are used. Becauseof this, a guest-host liquid-crystal composition having a high orderparameter has been difficult to realize.

DISCLOSURE OF THE INVENTION

An object of the present invention is (1) to provide a dichroic dyewhich is reduced in the drawbacks described above and is excellent instructural safety and dichroism. Another object of the present inventionis (2) to provide, using the dye, a guest-host liquid-crystalcomposition and a liquid-crystal display element, which have hues suchas black, brown, dark blue, etc., and having a high order parameterthroughout the whole light absorption wavelength range.

As a result of extensive studies made by the present inventors in viewof subject (1) described above, they have found that a tetrakisazo dyesynthesized from 2,2'-ditrifluoromethylbenzidine, which singularly showsno mutagenicity despite the fact that it is a benzidine compound, and aphenolic coupling ingredient is a yellow dye which is highly safe andhas exceedingly high dichroism and which is superior in dichroism to thetrisazo dyes described in U.S. Pat. No. 4,610,803, cited hereinabove.The present invention has been completed based on this finding.

An essential point of the present invention resides in a dichroic azodye which has a trifluoromethyl-substituted biphenyl framework and isrepresented by the following general formula I!: ##STR4## (wherein A andB each independently represents an optionally substituted alkyl group,phenyl group or cyclohexyl group; X and X¹ each independently representsa methylene group or a carbonyl group; and R₁ to R₁₂ each independentlyrepresents a hydrogen atom, a halogen atom, a methyl group or a methoxygroup, or R₂ and R₃, R₅ and R₆, R₈ and R₉, and R₁₁ and R₁₂ may be bondedto each other to form an aliphatic, aromatic or nitrogenous aromaticring which is a five-membered or larger membered ring).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plot of absorbance (relative value) versus wavelength (nm)for the cell fabricated in Example 21. (GH liquid-crystal composition1).

FIG. 2 is a plot of absorbance (relative value) versus wavelength (nm)for the cell fabricated in Example 22. (GH liquid-crystal composition2).

FIG. 3 is a plot of absorbance (relative value) versus wavelength (nm)for the cell fabricated in Example 23. (GH liquid-crystal composition3).

As a result of extensive investigations further made by the presentinventors in view of subject (2) described above, they have found thatwhen the above yellow dye having a biphenyl framework is used incombination with dichroic dyes each having a specific structure toprepare a guest-host liquid-crystal composition having hues such asblack, brown and dark brown, this composition has a high order parameterthroughout the whole light absorption wavelength range. Accordingly, thesecond essential point of the present invention resides in a guest-hostliquid-crystal composition and a liquid-crystal display elementcomprising the guest-host liquid-crystal composition, which contain atleast one dichroic azo dye represented by general formula I! describedabove, which are characterized in that they contain at least one dyeselected from Group (A) shown below at least one dye selected from Group(B) shown below, and at least one dye selected from Group (C) shownbelow:

Group (A)

dichroic azo dyes represented by general formula I! described above;

Group (B)

dichroic azo dyes having a trifluoromethyl-substituted biphenylframework and represented by the following general formulae II! andIII!: ##STR5## (wherein A¹ and B¹ each represents a hydrogen atom or anonionic substituent; X² and X³ each represents ##STR6## Z¹ to Z¹⁶ eachrepresents a hydrogen atom, a halogen atom, a methyl group or a methoxygroup, or Z¹ and Z², Z⁴ and Z⁵, Z⁷ and Z⁸, Z¹⁰ and Z¹¹, and Z¹³ and Z¹⁴are bonded to each other to form an aliphatic, aromatic or nitrogenousaromatic ring which is a five-member or larger-membered ring; and m andn each represents a number of 0 to 2); ##STR7## wherein A², A³, B² andB³ each represents a hydrogen atom, an alkyl group, an alkoxyalkylgroup, an optionally substituted aralkyl group, or afluoroalkyl-substituted alkyl group, or A² and A³ are bonded to eachother and B² and B³ are bonded to each other to thereby each form afive-membered or larger-membered nitrogenous aliphatic ring; Z²¹ to Z³²each represents a hydrogen atom, a halogen atom, a methyl group or amethoxy group, or Z²¹ and Z²², Z²⁴ and Z²⁵, Z²⁷ and Z²⁸, and Z³⁰ and Z³¹are bonded to each other to form an aliphatic, aromatic or nitrogenousaromatic ring which is a five-membered or larger-membered ring; or A²and Z²³, A³ and Z²¹, B² and Z³², and B³ and Z³¹ are bonded to each otherto form a five-membered or large -membered nitrogenous aliphatic ring;and p and q each represents a number of 0 to 2 (provided that the casewhere both p and q are 0 is excluded)!;

Group (C)

dichroic azo dyes represented by the following general formula IV! anddichroic anthraquinone dyes represented by the following general formulaV!: ##STR8## (wherein --X⁴ -- represents a single bond, --OCO-- or--S--; A⁴ represents a hydrogen atom, an alkyl or alkoxy group having 1to 10 carbon atoms, an alkoxyalkyl group having 2 to 12 carbon atoms, ahalogen atom, a haloalkyl group, a haloalkoxy group, a haloalkoxyalkylgroup, or a phenyl, cyclohexylphenyl or benzyl group optionally having asubstituent selected from these alkyl, alkoxy and alkoxyalkyl groups;and B⁴ represents a hydrogen atom, an alkyl or alkoxy group having 1 to10 carbon atoms, an alkoxyalkyl group having 2 to 12 carbon atoms, ahalogen atom, e.g., a fluorine or chlorine atom, or a cyclohexyl,phenyl, benzyl or cyclohexylmethyl group optionally having a substituentselected from these alkyl, alkoxy and alkoxyalkyl groups and halogenatoms); ##STR9## (wherein ##STR10## represents ##STR11## and B⁵ and B⁶each independently represents a hydrogen atom, a halogen atom, a line orbranched alkyl or alkoxy group having 1 to 10 carbon atoms, a linear orbranched alkoxyalkyl group having 2 to 12 carbon atoms, or a cyclohexylor phenyl group optionally having a substituent selected from thesealkyl, alkoxy and alkoxyalkyl groups).

The azo dye represented by general formula I!, which has atrifluoromethyl-substituted biphenyl framework, can be synthesized asfollows. 2,2'-Ditrifluoromethylbenzidine is subjected to a knowndiazotizing coupling reaction with compounds VI! and VII! shown below(in the formulae, R₄ to R₉ have the same meanings as those in generalformula I! given above, and R₁₃ and R₁₄ represent a hydrogen atom or--CH₂ SO₃ Na). In the case where R₁₃ and R₁₄ are --CH₂ SO₃ Na, thecoupling reaction product is hydrolyzed. Thus, a compound represented bythe following general formula VIII! (wherein R₄ to R₉ have the samemeanings as those in general formula I! given above) is obtained.Subsequently, this compound represented by general formula VIII! isreacted with a phenolic coupler by diazotizing coupling reaction toobtain a compound represented by the following general formula IX!(wherein R₁ to R₁₂ have the same meanings as those in general formula I!given above). This compound is then etherified or esterified at bothends thereof by a known method to incorporate the groups A--X-- and --X¹--B to thereby obtain the objective dye. ##STR12##

MODES FOR CARRYING OUT THE INVENTION

In general formula I! given above, A and B each independently ispreferably an alkyl group having 1 to 8 carbon atoms, a phenyl group, acyclohexyl group, or a cycloalkyl or phenyl group substituted with

a halogen atom, a trifluoromethyl group, a trifluoromethoxy group, analkyl group, an alkoxy group, an alkoxyalkyl group, an optionallysubstituted cycloalkyl or phenyl group.

Preferably, A and B each independently represents a phenyl or cyclohexylgroup substituted with a substituent selected from

alkyl groups such as lower alkyl groups (having, e.g., 1 to 4 carbonatoms),

alkoxy groups such as alkoxy groups having 1 to 4 carbon atoms,

alkoxyalkyl groups such as alkoxyalkyl groups having 2 to 4 carbonatoms, and

cyclohexyl and phenyl groups optionally substituted with an alkyl grouphaving not more than 6 carbon atoms.

R₁ to R₁₂ are defined in accordance with the following (1) and (2).

(1) R₁, R₄, R₇ and R₁₀ each independently is selected from a hydrogenatom, halogen atoms, a methyl group and a methoxy group.

Each of them preferably is a hydrogen atom.

(2) R₂, R₃, R₅, R₆, R₈, R₉, R₁₁ and R₁₂ each independently is selectedfrom a hydrogen atom, halogen atoms, a methyl group and a methoxy groupas in (1) above; or R₂ and R₃, R₅ and R₆, R₈ and R₉, and R₁₁ and R₁₂ arebonded to each other to form an aliphatic, aromatic, or nitrogenousaromatic ring which is a five-membered or larger-membered ring.

In the case where R₂ and R₃, R₅ and R₆, R₈ and R₉, and R₁₁ and R₁₂ eachform a ring, this ring is preferably a five-membered or larger-memberedring from the standpoint of structural stability, and most desirablyconstitutes a part of a tetralin, naphthalene or quinoline ring.

The rings which are formed by R₂ and R₃, R₅ and R₆, R₈ and R₉, and R₁₁and R₁₂ bonded to each other may be substituted. Preferred substituentsare alkyl groups, alkoxy groups and halogen atoms. More preferredsubstituents are alkyl groups having 1 to 4 carbon atoms, alkoxy groupshaving 1 to 4 carbon atoms, a chlorine atom, and a bromine atom. Mostpreferred substituents are alkyl groups having 1 to 4 carbon atoms.

Specific examples of the dye represented by general formula I! are shownin Table 1.

In Compound I-10 given in Table 1, the nitrogen atom of each of thequinoline ring formed by R₅ and R₆ and that formed by R₈ and R₉ islocated apart from the biphenyl structure as shown below. ##STR13##

                                      TABLE 1                                     __________________________________________________________________________    Struc-                                                                        tural                                                                         formula                                                                           A            X    R.sup.1                                                                          R.sup.4                                                                          R.sup.5                                                                          R.sup.6                                                                         R.sup.7                                                                          R.sup.8                                                                          R.sup.9                                                                          R.sup.11                                                                         X.sup.1                                                                            B                           __________________________________________________________________________    I-1                                                                                ##STR14##   CH.sub.2                                                                           CH.sub.3                                                                         CH.sub.3                                                                         H  H H  CH.sub.3                                                                         H  CH.sub.3                                                                         CH.sub.2                                                                            ##STR15##                  I-2                                                                                ##STR16##   CH.sub.2                                                                           CH.sub.3                                                                         CH.sub.3                                                                         H  H H  CH.sub.3                                                                         H  CH.sub.3                                                                         CH.sub.2                                                                            ##STR17##                  I-3                                                                                ##STR18##   CH.sub.2                                                                           H  H  bonded to form part of naphtha- lene                                               Hing                                                                             bonded to form part of naphtha- lene                                          ring  H  CH.sub.2                                                                            ##STR19##                  I-4                                                                                ##STR20##   CO   H  H  H  H H  H  H  H  CO                                                                                  ##STR21##                  I-5                                                                                ##STR22##   CH.sub.2                                                                           H  CH.sub.3                                                                         H  H H  CH.sub.3                                                                         H  H  CH.sub.2                                                                            ##STR23##                  I-6                                                                                ##STR24##   CH.sub.2                                                                           H  Cl H  H H  Cl H  H  CH.sub.2                                                                            ##STR25##                  I-7                                                                                ##STR26##   CH.sub.2                                                                           H  H  H  H H  H  H  H  CH.sub.2                                                                            ##STR27##                  I-8                                                                                ##STR28##   CH.sub.2                                                                           H  CH.sub.3                                                                         CH.sub.3                                                                         H CH.sub.3                                                                         CH.sub.3                                                                         H  H  CH.sub.2                                                                            ##STR29##                  I-9                                                                                ##STR30##   CH.sub.2                                                                           H  CH.sub.3                                                                         H  H H  CH.sub.3                                                                         H  H  CH.sub.2                                                                            ##STR31##                  I-10                                                                               ##STR32##   CH.sub.2                                                                           H  H  bonded to form part of quino- lene                                                 Hing                                                                             bonded to form part of quino- lene                                            ring  H  CH.sub.2                                                                            ##STR33##                  I-11                                                                               ##STR34##   CH.sub.2                                                                           H  H  bonded to form part of naphtha- lene                                               Hing                                                                             bonded to form part of naphtha- lene                                          ring  H  CH.sub.2                                                                            ##STR35##                  I-12                                                                              C.sub.7 H.sub.15 (n)                                                                       CH.sub.2                                                                           H  H  H  H H  H  H  H  CH.sub.2                                                                           C.sub.7 H.sub.15 (n)        I-13                                                                               ##STR36##   CH.sub.2                                                                           H  CH.sub.3                                                                         H  H H  CH.sub.3                                                                         H  H  CH.sub.2                                                                            ##STR37##                  I-14                                                                               ##STR38##   CH.sub.2                                                                           H  H  bonded to form part of tetralin ring                                               H  bonded to form part of tetralin                                                     Hing                                                                             CH.sub.2                                                                            ##STR39##                  I-15                                                                               ##STR40##   CH.sub.2                                                                           H  CH.sub.3                                                                         H  H H  CH.sub.3                                                                         H  H  CH.sub.2                                                                            ##STR41##                  I-16                                                                               ##STR42##   CH.sub.2                                                                           CH.sub.3                                                                         H  bonded to form part of naphtha- lene                                               Hing                                                                             bonded to form part of naphtha- lene                                          ring  CH.sub.3                                                                         CH.sub.2                                                                            ##STR43##                  I-17                                                                               ##STR44##   CH.sub.2                                                                           H  CH.sub.3                                                                         H  H H  CH.sub.3                                                                         H  H  CH.sub.2                                                                            ##STR45##                  I-18                                                                               ##STR46##   CO   H  H  H  H H  H  H  H  CO                                                                                  ##STR47##                  I-19                                                                               ##STR48##   CO   H  H  bonded to form part of naphtha- lene                                               Hing                                                                             bonded to form part of naphtha- lene                                          ring  H  CO                                                                                  ##STR49##                  __________________________________________________________________________

In the case where the dye represented by general formula I! alone or incombination with other dyes is mixed with an appropriate liquid-crystalcompound and the resulting mixture is used as a guest-hostliquid-crystal composition, the total incorporation amount of the dye(s)is usually from 0.05 to 15% by weight, preferably from 0.5 to 5% byweight, based on the weight of the liquid-crystal composition.

By mixing the yellow dichroic dye of the present invention with dyesselected from Groups (B) and (C) described above and with aliquid-crystal composition, a composition having a high order parameterthroughout the whole light absorption wavelength range can be prepared.

In general formula II!, A¹ and B¹ represent a hydrogen atom or anonionic substituent. Examples of the nonionic substituent include alkylgroups, alkoxyalkyl groups, alkoxy groups, alkoxyalkoxy groups,##STR50## a cyano group, a nitro group, halogen atoms, --CF₃, --OCF₃,--OCF₂ H, --OCF₂ CF₂ H, and a phenyl or cyclohexyl group substitutedwith an alkyl group, an alkoxyalkyl group or an alkoxy group.

Preferred examples of A¹ and B¹ include a hydrogen atom, halogen atoms,--CF₃, --OCF₃, --OCF₂ H, --OCF₂ CF₂ H, alkyl groups, alkoxyalkyl groups,alkoxy groups, ##STR51## and a phenyl or cyclohexyl group substitutedwith an alkyl group, an alkoxyalkyl group or an alkoxy group. Morepreferred examples thereof include alkyl groups, alkoxyalkyl groups,alkoxy groups, and a phenyl or cyclohexyl group substituted with analkyl group, an alkoxyalkyl group or an alkoxy group.

In the above formulae, R^(a) represents an alkyl group; R^(b) representsan alkylene group; R^(c) represents an alkyl group containing one ormore halogen atoms; and R^(d) and R^(e) represent a hydrogen atom, ahalogen atom, a methoxy group, a trifluoromethyl group, an alkyl group,or a nitro group.

Specific examples thereof include C₁₋₁₈ alkyl groups such as methyl,ethyl, and linear or branched propyl, butyl, hexyl and octyl; C₂₋₁₈alkoxyalkyl groups such as ethoxymethyl, butoxymethyl, ethoxyethyl andbutoxyethyl; alkoxy groups especially those of C₁₋₁₈ such as methoxy,ethoxy, and linear or branched propoxy, butoxy and heptyloxy;alkyl-substituted phenyl groups such as butylphenyl and hexylphenyl;alkoxyalkyl-substituted phenyl groups such as ethoxymethylphenyl andbutoxyethylphenyl; alkoxy-substituted phenyl groups such aspropoxyphenyl and hexyloxyphenyl; alkyl-substituted cyclohexyl groupssuch as butylcyclohexyl and octylcyclohexyl; and alkoxy-substitutedcyclohexyl groups such as pentoxycyclohexyl. Examples of the halogenatom include a fluorine atom, a bromine atom and a chlorine atom.

R^(f) represents a hydrogen atom, a halogen atom, a methoxy group, atrifluoromethyl group or an alkyl group. Examples of the grouprepresented by: ##STR52## include benzyloxy; benzyloxy groupssubstituted with a halogen atom, such as p-chlorobenzyloxy andp-fluorobenzyloxy; a p-methoxybenzyloxy group; benzyloxy groupssubstituted with a linear or branched C₁₋₆ alkyl group, such asp-methylbenzyloxy and p-t-butylbenzyloxy; andp-trifluoromethylbenzyloxy.

X² and X³ are preferably ##STR53##

Z¹ to Z¹⁶ are preferably such that Z³, Z⁶, Z⁹, Z¹² and Z¹³ to Z¹⁶ are ahydrogen atom and Z¹, Z², Z⁴, Z⁵, Z⁷, Z⁸, z¹⁰, and Z¹¹ each is ahydrogen atom, a halogen atom, a methyl group or a methoxy group.

In the case where Z¹ and Z², Z⁴ and Z⁵, Z⁷ and Z⁸, Z¹⁰ and Z¹¹, and Z¹³and Z¹⁴ are bonded to each other to form a five-membered orlarger-membered ring, this ring preferably constitutes a part of atetralin, naphthalene or quinoline ring.

Symbols m and n each represents an integer of 0 to 2. The sum of m and nis preferably from 1 to 4. It is especially preferred that m and n eachbe 1 from the standpoints of synthesis and practical use.

In general formula III!, A², A³, B² and B³ are preferably such that A²and B² represent a hydrogen atom, a methyl group or an ethyl group andA³ and B³ are an alkyl group, an alkoxyalkyl group, an optionallysubstituted aralkyl group, or a fluoroalkyl-substituted alkyl group.Examples of A³ and B³ include C₁₋₈ alkyl groups such as methyl, ethyl,and linear or branched propyl, butyl, hexyl, octyl, dodecyl andoctadecyl; C₂₋₁₈ alkoxyalkyl groups such as ethoxymethyl, butoxymethyl,ethoxyethyl and butoxyethyl; aralkyl groups optionally substituted withan alkyl group, an alkoxy group, a halogen atom or the like, such asbenzyl, phenethyl, 4-butylbenzyl, 4-pentoxybenzyl and 4-chlorobenzyl;and fluoroalkyl-substituted alkyl groups such as perfluorobutylethyl andperfluorohexylethyl.

In the case where A² and A³ are bonded to each other and B² and B³ arebonded to each other to thereby each form a five-membered orlarger-membered ring, these rings each preferably constitutes a part ofa pyrrolidine, piperidine, or morpholine ring.

Z²¹ to Z³² are preferably such that Z²¹, Z²³, Z²⁶, Z²⁹, Z³⁰ and Z³²represent a hydrogen atom and Z²², Z²⁴, Z²⁵, Z²⁷, Z²⁸ and Z³¹ eachrepresents a hydrogen atom, a halogen atom such as a fluorine, bromineor chlorine atom, a methyl group, or a methoxy group.

In the case where Z²¹ and Z²², Z²⁴ and Z²⁵, Z²⁷ and Z²⁸, and Z³⁰ and Z³¹are bonded to each other, preferably Z²⁴ and Z²⁵ are bonded to eachother and Z³⁰ and Z³¹ are bonded to each other, to thereby each form afive-membered or larger-membered membered ring, these rings eachpreferably constitutes a part of a tetralin, naphthalene or quinolinering.

Furthermore, in the case where A² and Z²³, A³ and Z²¹, B² and Z³², or B³and Z³¹ are bonded to each other to form a five-membered orlarger-membered ring, these rings each preferably constitutes a part ofa julolidine or tetrahydroquinoline ring.

Symbols p and q each represents a number of 0 to 2, provided that thecase where both p and q are 0 is excluded. It is especially preferredthat p and q represent the same number, specifically 1 or 2, from thestandpoint of practical use.

Preferred examples of A⁴ and B⁴ in general formula IV! and of B⁵ and B⁶in general formula V! include alkyl groups having 1 to 10 carbon atomssuch as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl andnonyl; alkoxy groups having 1 to 10 carbon atoms and each correspondingto the respective alkyl groups described above; alkoxyalkyl groupshaving 2 to 12 carbon atoms such as methoxymethyl, methoxyethyl,methoxybutyl, ethoxymethyl, ethoxyethyl and ethoxybutyl; and halogenatoms such as fluorine, chlorine and bromine atoms. Although thesealkyl, alkoxy and alkoxyalkyl groups may be linear or branched, they arepreferably linear from the standpoint of dichroism.

Specific examples of the compounds represented by general formulae II!to V! are shown in Table 2.

                                      TABLE 2                                     __________________________________________________________________________     ##STR54##                                                                    Structural formula            A.sup.1                                                                            B.sup.1                                    __________________________________________________________________________    II-1                          H.sub.5 C.sub.2 O                                                                  C.sub.5 H.sub.11                           II-2                          H.sub.5 C.sub.2 O                                                                  OC.sub.2 H.sub.5                           II-3                          H.sub.11 C.sub.5                                                                   C.sub.5 H.sub.11                           II-4                          H.sub.9 C.sub.4 O                                                                  C.sub.5 H.sub.11                           __________________________________________________________________________     ##STR55##                                                                    Structural formula A.sup.2                                                                            A.sup.3          B.sup.2                                                                            B.sup.3                         __________________________________________________________________________    III-1              H.sub.5 C.sub.2                                                                    H.sub.5 C.sub.2  C.sub.2 H.sub.5                                                                    C.sub.2 H.sub.5                 III-2              H.sub.11 C.sub.5                                                                   H.sub.11 C.sub.5 C.sub.5 H.sub.11                                                                   C.sub.5 H.sub.11                III-3              H.sub.9 C.sub.4                                                                    H.sub.9 C.sub.4  C.sub.5 H.sub.11                                                                   C.sub.5 H.sub.11                __________________________________________________________________________     ##STR56##                                                                    Structural formula                                                                      X.sup.4      A.sup.4           B.sup.4                              __________________________________________________________________________    IV-1      OCO                                                                                         ##STR57##        C.sub.8 H.sub.17                     IV-2      OCO                                                                                         ##STR58##        C.sub.6 H.sub.13                     IV-3      OCO                                                                                         ##STR59##                                                                                       ##STR60##                           IV-4      OCO                                                                                         ##STR61##                                                                                       ##STR62##                           IV-5      OCO                                                                                         ##STR63##                                                                                       ##STR64##                           IV-6      OCO                                                                                         ##STR65##                                                                                       ##STR66##                           IV-7      OCO                                                                                         ##STR67##                                                                                       ##STR68##                           IV-8      single bond  C.sub.8 H.sub.17 (n)                                                                             ##STR69##                           IV-9      S            C.sub.2 F.sub.5                                                                                  ##STR70##                           __________________________________________________________________________     ##STR71##                                                                     Structural formula                                                                         ##STR72##                                                                                          ##STR73##                                                                                 ##STR74##                      __________________________________________________________________________    V-1                                                                                         ##STR75##                                                                                          ##STR76##                                                                                 ##STR77##                      V-2          C.sub.4 H.sub.9      H                                                                                          ##STR78##                      V-3          C.sub.4 H.sub.9      C.sub.4 H.sub.9                                                                            ##STR79##                      V-4          H                                                                                                   ##STR80##                                                                                 ##STR81##                      V-5          C.sub.4 H.sub.9                                                                                     ##STR82##                                                                                 ##STR83##                      __________________________________________________________________________

In the guest-host liquid-crystal composition of the present invention,the use amounts of dyes of Groups (A), (B) and (C) may be appropriatelydecided depending on the hue to be obtained. In general, however, theuse amount of dye (A) is from 0.2 to 3.0% by weight, that of dye (B) isfrom 0.1 to 3.0% by weight, and that of dye (C) is from 0.2 to 11% byweight, based on the weight of the liquid-crystal composition, and thetotal amount of these dyes is from 0.5 to 15% by weight, preferably from0.5 to 5% by weight, based on the weight of the liquid-crystalcomposition.

Examples of the liquid-crystal compound for use in the liquid-crystalcomposition of the present invention include those shown in Table 3below.

                                      TABLE 3                                     __________________________________________________________________________     ##STR84##                                                                     ##STR85##                                                                     ##STR86##                                                                     ##STR87##                                                                     ##STR88##                                                                     ##STR89##                                                                     ##STR90##                                                                    __________________________________________________________________________

(In the formulae, V and W each represents an alkyl group, an alkoxygroup, an alkoxyalkyl group, an alkylphenyl group, an alkoxyalkylphenylgroup, an alkoxyphenyl group, an alkylcyclohexyl group, analkoxyalkylcyclohexyl group, an alkylcyclohexylphenyl group, acyanophenyl group, a cyano group, a halogen atom, a fluoromethyl group,a fluoromethoxy group, an alkylphenylalkyl group, an alkoxyphenylalkylgroup, an alkylcyclohexylalkyl group, an alkoxyalkoxycyclohexylalkylgroup, an alkoxyphenylalkyl group or an alkylcyclohexylphenylalkylgroup. These alkyl chains and alkoxy chains may contain a center ofoptical activity. Y represents a hydrogen atom, a halogen atom or acyano group. The phenyl or phenoxy group which can be contained in V andW may be further substituted with a cyano group or a halogen atom suchas fluorine and chlorine atoms. The phenyl group contained in the abovestructural formulae each may be further substituted with from one tofour substituents selected from halogen atoms such as fluorine andchlorine atoms and a cyano group.)

Recently, the so-called fluorinated liquid-crystal compounds, which havea substituent such as a fluorine atom or a fluorinated group, e.g., --F,--CF₃ and --OCF₃, are advantageously used in TFT LCDs (thin-filmtransistor liquid-crystal displays) and the like in place ofconventional cyano-containing liquid-crystal compounds. The dyes ofGroups (A), (B), and (C) according to the present invention areexcellent in, e.g., compatibility with these fluorinated liquid-crystalcompounds.

The liquid-crystal composition of the present invention may contain anoptically active compound which may exhibit a liquid-crystal phase orneed not exhibit it, such as, e.g., cholesteryl nonanoate. It mayfurther contain various additive ingredients including ultravioletabsorbers and antioxidants.

By sandwiching the thus-obtained liquid-crystal composition between twoelectrode-possessing substrates at least one of which is transparent, aliquid-crystal display element utilizing a guest-host effect (see, forexample, Shoich Matsumoto and Nagayoshi Sumida, Ekisho No SaishinGijutsu (The Newest Liquid-Crystal Technology), Kogyo Chosakai, 34(1983); and J. L. Fergason, SID 85 Digest, 68 (1983)) or the like can beconstituted.

Examples of the transparent electrode substrate usually include glassplates and plates of various synthetic resins including acrylic resins,polycarbonate resins and epoxy resins. An electrode layer is formed onthe substrate. The transparent electrode layer is usually made of ametal oxide such as, e.g., indium oxide, indium-tin oxide (ITO) or tinoxide. That surface of the transparent electrode layer which is to be incontact with a liquid crystal may be subjected to an alignmenttreatment, if desired. Examples of methods for the alignment treatmentinclude: a method comprising applyingoctadecyldimethyl(3-(trimethoxysilyl)propyl)ammonium chloride,hexadecyltrimethylammonium bromide or the like to conduct verticalalignment; a method comprising applying a polyimide to conduct parallelalignment; a method comprising rubbing the surface with a cotton cloth,absorbent cotton or the like to conduct parallel alignment; and a methodcomprising slantwise vapor-depositing an SiO_(x) to conduct parallelalignment. These methods may be appropriately used.

Two substrates are united via a spacer or the like in such a manner thatthe electrode surfaces which have undergone an alignment treatment faceeach other at a distance of from 1 to 50 μm, preferably from 1 to 15 μm,to fabricate an element (cell) having a space. The liquid crystal ispacked into the space, and the resulting structure is sealed.

BEST MODES FOR CARRYING OUT THE INVENTION

The present invention will be explained below in detail by reference toExamples.

The present invention should not be construed as being limited to theseExamples, unless the invention departs from the spirit thereof.

EXAMPLE 1!

Into 2.2 ml of 35% hydrochloric acid and 40 ml of ice water wasdissolved 1.6 g of 2,2'-ditrifluoromethylbenzidine, represented by thefollowing structural formula. ##STR91## To this solution was added 0.73g of sodium nitrite with stirring.

After the mixture was stirred at from 0° to 5° C. for 1 hour, sulfamicacid was added thereto to decompose an excess nitrite. Thus, diazosolution 1 was prepared.

On the other hand, a coupler solution was prepared by dissolving 2.3 gof sodium m-toluidinomethanesulfonate into 50 ml of water. Diazosolution 1 was gradually added thereto while stirring the couplersolution with cooling at from 0° to 5° C. and regulating the pH thereofin the range of from 4 to 7 with an aqueous sodium acetate solution.This mixture was reacted at the temperature for 2 hours.

After the reaction, the reaction product was taken out by filtration andwashed with water. The cake obtained was boiled together with a 3%aqueous sodium hydroxide solution to thereby hydrolyze the cake. Theyellow dye precipitated was taken out by filtration and washed withwater until the washing water became neutral. Thus, a bisazo compoundrepresented by the following structural formula was obtained. ##STR92##

Into 40 ml of N-methylpyrrolidone was dissolved 2.7 g of the bisazocompound. Thereto was added 2.6 ml of 35% hydrochloric acid. After thismixture was cooled to from 0° to 5° C., 1.1 g of sodium nitritedissolved in a small amount of water was added to conduct diazotization(to obtain diazo solution 2). To this diazo solution 2 was added 1.6 gof m-cresol dissolved in 10 ml of N-methylpyrrolidone. The pH of thismixture was adjusted to from 8 to 9 with an aqueous sodium hydrogencarbonate solution. Water was added at 2 hours after, and the resultingprecipitate was taken out by filtration and then purified by columnchromatography to obtain the tetrakisazo compound represented by thefollowing structural formula. ##STR93##

Into 20 ml of N-methylpyrrolidone was dissolved 1.0 g of the tetrakisazocompound. Thereto were added 0.5 g of potassium carbonate and 0.5 g of4-methylbenzyl chloride as an etherifying agent. After this mixture wasreacted at from 70° to 80° C. for 4 hours, methanol was added. Theresulting precipitate was taken out by filtration, and the crudecrystals obtained were purified by column chromatography. Thus, theobjective azo dye represented by the following structural formula wasobtained, which is I-1 shown in Table 1. ##STR94##

This azo dye was dissolved into the fluorinated liquid-crystal mixturecommercially available under the trade name of ZLI-4792 (product of E.MERCK Co.) in a concentration of 1% by weight to prepare a yellowguest-host liquid-crystal composition. This composition was packed intoa cell having a gap width of 9 μm and comprising two glass substratesfacing each other and each having a transparent electrode which hadundergone a treatment for liquid-crystal parallel alignment whichtreatment comprises applying a polyimide resin, curing the same, andrubbing the cured resin. The cell was then sealed.

This yellow-colored cell was examined for its absorbance with respect toa linear polarized light parallel to the alignment direction (A//) ofthe cell and for its absorbance with respect to linear polarized lightperpendicular to the alignment direction (A⊥) of the cell. The orderparameter (S) at the absorption peak thereof (λ_(max) : 413 nm) wasdetermined using the following equation.

    S=(A//-A⊥)/(A//+2A⊥)

As a result, it was found that S=0.79.

EXAMPLE 2!

The same synthesis procedure as in Example 1 was conducted, except that4-pentylbenzyl chloride was used as an etherifying agent in place of4-methylbenzyl chloride. Thus, the tetrakisazo dye represented by thefollowing structural formula was obtained, which is I-2 shown inTable 1. ##STR95##

Using this dye, a yellow-colored liquid-crystal cell was fabricated inthe same manner as the above. The cell thus obtained was examined fororder parameter (S) in the same manner as in Example 1. As a result, itwas found that S=0.80 (λ_(max) : 413 nm).

EXAMPLE 3!

The same diazo solution 1 as in Example 1 was prepared.

On the other hand, a coupler solution was prepared by dissolving 1.8 gof α-naphthylamine hydrochloride into 30 ml of water and 60 ml of aceticacid. The diazo solution was added thereto while stirring the couplersolution with cooling at from 0° to 5° C. This mixture was graduallyheated to room temperature, and reacted at the temperature for 2 hours.

After the reaction, the reaction mixture was diluted with water, and theresulting precipitate was taken out by filtration and washed with water.Thus, a bisazo compound represented by the following structural formulawas obtained. ##STR96##

Into 40 ml of N-methylpyrrolidone was dissolved 1.3 of the bisazocompound. Thereto was added 1.1 ml of 35% hydrochloric acid. After thismixture was cooled to from 0° to 5° C., 0.3 g of sodium nitritedissolved in a small amount of water was added to conduct diazotization(to obtain diazo solution 3). To this diazo solution 3 was added 0.4 gof phenol dissolved in 10 ml of N-methylpyrrolidone. The pH of theresulting mixture was adjusted to from 8 to 9 with an aqueous sodiumhydrogen carbonate solution. Water was added at 2 hours after, and theresulting precipitate was taken out by filtration and then purified bycolumn chromatography to obtain the tetrakisazo compound represented bythe following structural formula. ##STR97##

Into 20 ml of N-methylpyrrolidone was dissolved 0.20 g of thetetrakisazo compound. Thereto were added 0.13 g of potassium carbonateand 0.19 g of 4-pentylbenzyl chloride. The mixture thus obtained wasreacted at from 70° to 80° C. for 4 hours, and diluted with methanol.The resulting precipitate was taken out by filtration, and the crudecrystals obtained were purified by column chromatography. Thus, the azodye represented by the following structural formula was obtained, whichis I-3 shown in Table 1. ##STR98##

Using the azo dye thus obtained, a yellow-colored liquid-crystal cellwas fabricated in the same manner as in Example 1. The cell was examinedfor order parameter in the same manner as in Example 1. As a result, itwas found that S=0.82 (λmax: 469 nm).

EXAMPLE 4!

The bisazo compound obtained in Example 1 was reacted with phenol in thesame manner as in Example 3 to obtain the tetrakisazo compoundrepresented by the following structural formula. ##STR99##

Into 20 ml of N-methylpyrrolidone was dissolved 0.77 g of thetetrakisazo compound. Thereto were added 0.45 g of 4-cyclohexylbenzoylchloride and 0.4 g of triethylamine. This mixture was reacted at 60° C.for 2 hours. After cooling, the reaction mixture was diluted withmethanol. The resulting precipitate was taken out by filtration, and thecrude crystals obtained were purified by column chromatography. Thus,the azo dye represented by the following structural formula wasobtained, which is I-4 shown in Table 1. ##STR100##

Using the azo dye thus obtained, a yellow-colored liquid-crystal cellwas fabricated in the same manner as in Example 1. The cell was examinedfor order parameter in the same manner as in Example 1. As a result, itwas found that S=0.80 (λ_(max) : 398 nm).

EXAMPLES 5 TO 19!

Dyes I-5 to I-19, shown in Table 1, were synthesized according to themethods used in Examples 1 to 4. The order parameter (S) of each of thethus-obtained dyes in the fluorinated liquid-crystal mixturecommercially available under the trade name of ZLI-4792 (product of E.MERCK Co.) and the hue thereof are shown in Table 4 together with theresults of Examples 1 to 4 and that of the following ComparativeExample.

Comparative Example!

The same synthesis procedure as in Example 1 was conducted, except that2,2'-ditrifluoromethylbenzidine monodiazonium salt was used in place of2,2'-ditrifluoromethylbenzidine. Thus, the trisazo compound representedby the following structural formula was obtained. ##STR101## A coloredliquid-crystal cell was fabricated using the trisazo compound in thesame manner as in Example 1, and the order parameter thereof wasmeasured in the same manner as in Example 1. As a result, it was foundthat S=0.74, showing that the dye had poor dichroism.

                  TABLE 4                                                         ______________________________________                                        Example  Symbol in Table 1                                                                          S Value   Hue                                           ______________________________________                                         1       I-1          0.79      yellow                                         2       I-2          0.80      yellow                                         3       I-3          0.82      yellowish orange                               4       I-4          0.80      yellow                                         5       I-5          0.80      yellow                                         6       I-6          0.79      yellow                                         7       I-7          0.81      yellow                                         8       I-8          0.79      yellow                                         9       I-9          0.80      yellow                                        10       I-10         0.82      yellowish orange                              11       I-11         0.82      yellowish orange                              12       I-12         0.79      yellow                                        13       I-13         0.80      yellow                                        14       I-14         0.81      yellow                                        15       I-15         0.80      yellow                                        16       I-16         0.80      yellowish orange                              17       I-17         0.82      yellow                                        18       I-18         0.80      yellow                                        19       I-19         0.81      yellowish orange                              Comparative                                                                            --           0.74      yellow                                        Example                                                                       ______________________________________                                    

EXAMPLE 20!

The dyes obtained in Examples 1 to 4 were dissolved into a substitutedphenylcyclohexane liquid-crystal mixture, trade name ZLI-1132 (productof E. MERCK Co.; equivalent product with trade name TMC-1132) in thesame manner as in Example 1. The order parameters (S) thereof weremeasured in the same manner as in Example 1. The results obtained areshown in Table 5 below.

                  TABLE 5                                                         ______________________________________                                        Example No.  Order Parameter, S                                                                         λ.sub.max (nm)                               ______________________________________                                        1            0.79         414                                                 2            0.80         414                                                 3            0.81         471                                                 4            0.80         403                                                 ______________________________________                                    

EXAMPLE 21!

The following dichroic dyes described in Tables 1 and 2 were mixed withand dissolved into 100 g of a liquid-crystal mixture mainly composed offluorinated compounds and commercially available under the trade name ofZLI-4792 (manufactured by E. MERCK Co.) to prepare liquid-crystalcomposition I.

    ______________________________________                                                 I-3! 0.40 g                                                                   II-1!                                                                              0.25 g                                                                   IV-5!                                                                              0.66 g                                                                   IV-6!                                                                              0.38 g                                                          ______________________________________                                    

The liquid-crystal composition I thus prepared was packed into a cellcomprising transparent-electrode-possessing glass plates which hadundergone a treatment for homogeneous alignment comprising applying apolyimide resin, curing the same, and rubbing the cured resin, and whichwere disposed so that the surfaces that had undergone the alignmenttreatment faced each other. Thus, a liquid-crystal display element wasfabricated.

The colored cell thus obtained was examined for its absorbance withrespect to a linear polarized light parallel to the alignment direction(A//) of the cell and for its absorbance with respect to a linearpolarized light perpendicular to the alignment direction (A⊥) of thecell. The order parameters (S values) at absorption wavelengths thereofwere determined using the following equation.

    S value=(A//-A⊥)/(A//+2A⊥)

As a result, satisfactory values were obtained as shown in Table 6.

                  TABLE 6                                                         ______________________________________                                        Wavelength used                                                               for measurement                                                               (nm)          500    550        600  650                                      ______________________________________                                        S value       0.81   0.82       0.82 0.81                                     ______________________________________                                    

The absorbance spectrum with respect to A// of the cell fabricated isshown in FIG. 1.

EXAMPLE 22!

The following dichroic dyes shown in Tables 1 and 2 were mixed with anddissolved into 100 g of a liquid-crystal mixture mainly composed offluorinated compounds and commercially available under the trade name ofZLI-4792 (manufactured by E. MERCK Co.) to prepare liquid-crystalcomposition II.

    ______________________________________                                                 I-3!                                                                              0.40 g                                                                    II-1!                                                                             0.56 g                                                                    V-5!                                                                              2.40 g                                                           ______________________________________                                    

Thus prepared liquid-crystal composition II was packed into a cell inthe same manner as in Example 21 to fabricate a liquid-crystal displayelement.

The order parameters (S values) thereof were determined in the samemanner as in Example 21. As a result, satisfactory values were obtainedas shown in Table 7.

                  TABLE 7                                                         ______________________________________                                        Wavelength used                                                               for measurement                                                               (nm)          500    550        600  650                                      ______________________________________                                        S value       0.82   0.80       0.75 0.74                                     ______________________________________                                    

The absorbance spectrum with respect to A// of the cell fabricated isshown in FIG. 2.

EXAMPLE 23!

The following dichroic dyes shown in Tables 1 and 2 were mixed with anddissolved into 100 g of a liquid-crystal mixture mainly composed offluorinated compounds and commercially available under the trade name ofZLI-4792 (manufactured by E. MERCK Co.) to prepare liquid-crystalcomposition III.

    ______________________________________                                                 I-3! 0.35 g                                                                   II-1!                                                                              0.20 g                                                                   III-1!                                                                             0.22 g                                                                   IV-5!                                                                              0.30 g                                                                   V-5! 1.80 g                                                          ______________________________________                                    

Thus prepared liquid-crystal composition III was packed into a cell inthe same manner as in Example 21 to fabricate a liquid-crystal displayelement.

The order parameters (S values) thereof were determined in the samemanner as in Example 21. As a result, satisfactory values were obtainedas shown in Table 8.

                  TABLE 8                                                         ______________________________________                                        Wavelength used                                                               for measurement                                                               (nm)          500    550        600  650                                      ______________________________________                                        S value       0.82   0.82       0.78 0.76                                     ______________________________________                                    

The absorbance spectrum with respect to A// of the cell fabricated isshown in FIG. 3.

POSSIBILITY OF INDUSTRIAL APPLICATION

According to the dichroic dye of the present invention, which has highdichroism and high coloring power, and to liquid-crystal compositioncontaining the same, a display element excellent in contrast and otherperformances can be constituted.

We claim:
 1. A dichroic azo dye characterized by having atrifluoromethyl-substituted biphenyl framework and being represented bygeneral formula I!: ##STR102## (wherein A and B each independentlyrepresents an optionally substituted alkyl group, phenyl group orcyclohexyl group; X and X¹ each independently represents a methylenegroup or a carbonyl group; and R₁ to R₁₂ each independently represents ahydrogen atom, a halogen atom, a methyl group or a methoxy group, or R₂and R₃, R₅ and R₆, R₈ and R₉ and R₁₁ and R₁₂ may be bonded to each otherto form an aliphatic, aromatic or nitrogenous aromatic ring which is afive-membered or larger-membered ring).
 2. The dichroic azo dye asclaimed in claim 1, characterized in that in general formula I!, A and Beach independently is a phenyl or cyclohexyl group substituted with atleast one substituent selected from the group consisting of alkylgroups, alkoxyalkyl groups and alkoxy groups.
 3. A liquid-crystalcomposition characterized by comprising the dichroic dye as claimed inclaim 1 and a liquid-crystal compound.
 4. A liquid-crystal displayelement characterized by using the liquid-crystal composition as claimedin claim
 3. 5. A guest-host liquid-crystal composition containing adichroic dye, which is characterized in that the dichroic dyes compriseat least one dye selected from Group (A) shown below, at least one dyeselected from Group (B) shown below, and at least one dye selected fromGroup (C) shown below:Group (A) the dichroic azo dyes as claimed inclaim 1 or 2;Group (B) dichroic azo dyes represented by the followinggeneral formula II! or III! ##STR103## (wherein A¹ and B¹ eachrepresents a hydrogen atom or a nonionic substituent; X² and X³ eachrepresents ##STR104## Z¹ to Z¹⁶ each represents a hydrogen atom, ahalogen atom, a methyl group or a methoxy group, or Z¹ and Z², Z⁴ andZ⁵, Z⁷ and Z⁸, Z¹⁰ and Z¹¹, Z¹³ and Z₁₄ are bonded to each other to forman aliphatic, aromatic or nitrogenous aromatic ring which is afive-membered or larger-membered ring; and m and n each represents anumber 0 to 2) ##STR105## (wherein A², A³, B² and B³ each represents ahydrogen atom, an alkyl group, an alkoxyalkyl group, an optionallysubstituted aralkyl group or a fluoroalkyl-substituted alkyl group, orA² and A³ are bonded to each other and B² and B³ are bonded to eachother to thereby each form a five-membered or larger-memberednitrogenous aliphatic ring; Z²¹ to Z³² each represents a hydrogen atom,a halogen atom, a methyl group, or a methoxy group, or Z²¹ and Z²², Z²⁴and Z²⁵, Z²⁷ and Z²⁸, and Z³⁰ and Z³¹ are bonded to each other to forman aliphatic, aromatic or nitrogenous aromatic ring which is afive-membered or larger-membered ring; or A² and Z²³, A³ and Z²¹, B² andZ³², and B³ and Z³¹ are bonded to each other to form a five-membered orlarger-membered nitrogenous aliphatic ring; and p and q each representsa number of 0 to 2 (provided that the case where both p and q are 0 isexcluded));Group (C) dichroic azo dyes represented by the followinggeneral formula IV! and dichroic anthraquinone dyes represented by thefollowing general formula V! ##STR106## (wherein --X⁴ -- represents asingle bond, --OCO-- or --S--; A⁴ represents a hydrogen atom, an alkylor alkoxy group having 1 to 10 carbon atoms, an alkoxyalkyl group having2 to 12 carbon atoms, a halogen atom, a haloalkyl group, a haloalkoxygroup, a haloalkoxyalkyl group, or a phenyl, cyclohexylphenyl or benzylgroup optionally having a substituent selected from the alkyl, alkoxyand alkoxyalkyl groups described above; and B⁴ represents a hydrogenatom, an alkyl or alkoxy group having 1 to 10 carbon atoms, analkoxyalkyl group having 2 to 12 carbon atoms, a halogen atom, or acyclohexyl, phenyl, benzyl or cyclohexylmethyl group optionally having asubstituent selected from these alkyl, alkoxy and alkoxyalkyl groups andhalogen atoms) ##STR107## (wherein ##STR108## or ##STR109## and B⁵ andB⁶ each independently represents a hydrogen atom, a halogen atom, alinear or branched alkyl or alkoxy group having 1 to 10 carbon atoms, alinear or branched alkoxyalkyl group having 2 to 12 carbon atoms, or acyclohexyl or phenyl group optionally having a substituent selected fromthese alkyl, alkoxy and alkoxyalkyl groups).
 6. The guest-hostliquid-crystal composition as claimed in claim 5, characterized in thatin general formula I! for Group (A), A and B each independently is aphenyl or cyclohexyl group substituted with at least one substituentselected from the group consisting of alkyl groups, alkoxyalkyl groupsand alkoxy groups.
 7. A liquid-crystal display element characterized bycomprising the guest-host liquid-crystal composition as claimed in claim5 sandwiched between electrode-possessing substrates at least one ofwhich is transparent.